GEOFF BENNETT: The head of the U.N. nuclear watchdog visited Europe's largest nuclear plant today near the front lines in Southern Ukraine.

The Zaporizhzhia power plant is under Russian control and uses water from the Dnipro river to cool its reactors.

But a major dam near the plant was destroyed last week, potentially depriving it of that vital water.

Contingency measures to stabilize the plant are under way, while, elsewhere in Ukraine, a major counteroffensive is taking shape.

Emma Murphy of Independent Television News reports from the front lines.

EMMA MURPHY: They didn't start this war, but their hard fight is to end it.

This is Ukraine's counteroffensive, heavy weapons for heavy battles.

Their fight is hard and complicated with what they are fighting with.

This gun is from the 1980s, the ammunition from the 1950s.

It is unreliable and the fix is rudimentary.

How important is this counteroffensive?

OLEKSANDR, Senior Officer, 57th Brigade (through translator): It is very, very important, because we need to liberate the occupied territory of Ukraine, so civilians under Russian occupation can be brought back to Ukraine.

EMMA MURPHY: They hide their treasure well, then make its presence felt.

They're using heavy artillery like this to break down Russian infantry positions over the ridge just beyond there.

This counteroffensive will not be fast.

It will be slow, grinding and a fight for every single meter.

ITV News spent two days on the front line with Ukrainian forces.

Were they all soldiers or volunteers?

MAN: Different.

Different.

EMMA MURPHY: Different.

An army made up of professional soldiers and civilians who've become fighters.

Through fields reminiscent of battles past, they showed us the technology that has changed the way of warfare.

Drones have been absolutely crucial to the way this war has been waged.

And they will be even more important in the counteroffensive.

The unit commander tells me the drones allow them to find Russian positions up to two miles, then strike their men and their machinery.

They move on foot because vehicles are a target.

At the forward command base, the drones and artillery a coordinated.

What happens here drives the counteroffensive.

This base is very close to the fighting, and missiles fly above them continually.

Sergei explains how he receives information on the targets from the drone teams and coordinates the firing units.

And where is that place there?

Is that... SERGIE, Ukrainian Soldier: It's Bakhmut.

EMMA MURPHY: Bakhmut, right.

On the armored wall amid all the technology, someone has hung a Ukrainian prayer for soldiers.

They all pray for an end to this war, and know their work might hasten.

As we speak, another hit is called for.

Here, they are able to see the results of their work, watching the strikes in real time.

But Russia has the same power to survey an attack, so elaborate trenches lead to the Western weaponry so crucial to Ukraine's survival, pieces like this provided by Poland seven months ago.

They go out to fire, but there's a problem.

A Russian drone has been spotted.

Breaking cover risks being hit.

They pull back below the camouflage and hope.

While they wait for safer skies, they explain how they work and sleep in their position for days.

The Ukrainians won't say how many soldiers they have lost, but it's thought to be close to 20,000.

Every soldier knows the counterassault is much more dangerous than defense.

"This gun helps us slowly get back our land," Alexei says, but insists there's still a need for more weaponry and ammunition.

When finally the drone seems to be gone, they prepare to break cover once more.

They know after firing, it can be less than five minutes for the Russians to identify their position and hit back.

They have lost many colleagues that way, a note to take shelter.

Later, the commander sums up the mood of his troops.

OLEKSANDR (through translator): We are all trying our best, and we want all of this to finish as soon as possible.

We are doing everything to achieve it.

EMMA MURPHY: The counteroffensive won't end this war, but it will certainly shape the future of it.